In copending application Ser. No. 323,770, filed Jan. 15, 1973 now U.S. Pat. No. 3,859,789, a system is described for converting one type of energy into another type by means of a closed loop passageway containing a plurality of freely movable, mechanically unrestrained pistons, meaning that the pistons are not coupled to a mechanical element but can be propelled around the loop in much the same manner as a projectile. Successive ones of the pistons, preferably spheres having diameters slightly less than that of a tubular passageway through which they travel, are propelled in one direction around the passageway by application of a suitable force applied in a thrustor region of the passageway.
In one embodiment of the invention shown in that application, acceleration of the pistons is effected by means of an expanding fluid medium supplied externally to the closed loop passageway. After the pistons are thus accelerated, they pass through a second region where the kinetic energy of the traveling pistons is converted into another form of energy. This may be accomplished, for example, by forming the pistons from magnetically permeable material and by passing them through the magnetic field of a linear generator which converts the energy of the moving pistons into electrical energy. Alternatively, the kinetic energy of the moving pistons can be used to compress a gas or it can be converted into mechanical motion, for example, by causing successive ones of the pistons to strike radiallyextending blades on a rotatable paddle wheel.
Assuming that expansion of a gas is used to propel the pistons, they pass through a compressor region where the gas between them is compressed preparatory to a succeeding cycle of operation. This compressed gas from the compressor region is fed through a check valve to an external heater where energy in the form of heat is added to the gas, causing it to expand. The expanded gas is then used in a thrustor section following the compressor section to propel successive ones of the pistons around the closed loop passageway.
It has been found that when a piston enters the compressor section of the closed loop passageway with excessive kinetic energy, it may still have considerable kinetic energy by the time it passes the compressor outlet port when gas is lead through the aforesaid check valve to the external heater. Without the present invention, this situation is undesirable for two reasons. First, the residual kinetic energy of the piston is wasted and does not contribute to the compressor output. Secondly, a piston having excessive kinetic energy may strike other bodies in the compressor section with excessive velocity, thereby causing erratic and noisy operation. Furthermore, certain situations may arise wherein the pressure within the thrustor section exceeds that in the compressor section, meaning that pistons will tend to move from the thrustor section back into the compressor section, interfering with the compressor operation.